A new recipe for ΛCDM

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2017-04, Vol.77 (4), p.1-8
• Main Authors: Sahni, Varun, Sen, Anjan A.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics and Cosmology; Clustering; Cold dark matter; Dark energy; Dark matter; Elementary Particles; Equations of state; Gravitation; Hadrons; Heavy Ions; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Physics; Physics and Astronomy; Properties (attributes); Quantum Field Theories; Quantum Field Theory; Regular Article - Theoretical Physics; String Theory; Universe
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-017-4796-7

It is well known that a canonical scalar field is able to describe either dark matter or dark energy but not both. We demonstrate that a non-canonical scalar field can describe both dark matter and dark energy within a unified setting. We consider the simplest extension of the canonical Lagrangian L ∝ X α - V ( ϕ ) where α ≥ 1 and V is a sufficiently flat potential. In this case the kinetic term in the Lagrangian behaves just like a perfect fluid, whereas the potential term mimicks dark energy. For very large values, α ≫ 1 , the equation of state of the kinetic term drops to zero and the universe expands as if filled with a mixture of dark matter and dark energy. The velocity of sound in this model and the associated gravitational clustering are sensitive to the value of α . For very large values of α the clustering properties of our model resemble those of cold dark matter (CDM). But for smaller values of α , gravitational clustering on small scales is suppressed, and our model has properties resembling those of warm dark matter (WDM). Therefore our non-canonical model has an interesting new property: its expansion history resembles Λ CDM, while its clustering properties are akin to those of either cold or warm dark matter.